Apparatus for producing nitric oxide



H. A. HUMPHREY.

APPARATUS FOR PRODUCING NITRIC OXIDE.

APPLICATION FILED 05018, l98.

'1 429,035. PatentedSept. 12, 1922.

2 SHEETS-SHEET I.

INVENFUR HHJ/wmphrgy AHIURNEY H. A. HUMPHREY.

APPARATUS FOR PRODUCING NITRIC OXIDE.

APPLICATION FILED DEC. 1a. 1918.

1,429,035, PatentedSept. 12, 1922.

2 SHEETSSHEET 2,.

ERT ALFRED H'UMFHBEY, 6F LQNDON, ENGL.

A?EABATUS FOR PRODUCING Ni'TRIC QX'ITDLE.

Application filed Eleeemher 18, 1918. Serial No. 267,389.

T 0 all whom it may concern Be it known that l, HERBERT ALFRED HUMPHREY,a subject of the King of Great Britain and Ireland, and residing at TheMunitions Inventions Department Research Laboratory, University College,Gower Place, London, W. C. 1, England, have invented a certain new anduseful Improved Apparatus for Producing Nitric Oxide, of which thefollowing is a specification.

This invention relates to an apparatus for the production of nitricoxide by igniting an explosive gaseous mixture containing nitrogen andoxygen under suitable conditions so that the rise of temperature issufiicient to cause a portion of these two gases to combins in order toform nitric oxide.

As the result of my experience I have ascertained that in order thatsuch a process may result in a high yield of nitric oxide, the followingconditions should, as far as possihie, be fulfilled, namely (1) Thegaseous constituents should be measured and correctly proportioned andthe mixed combustible gases should be preheated before ignition to ashigh a degree as possible and preferably to such a point that themixture will ignite during compression.

(2) The highest possible temperature should be attained during theprocess.

(3) Subsequent to the attainment of the maximum temperature the gasesshould be cooled as rapidly as possible, both by expansion and by theperformance of external work, so that the nitric oxide formed may beprevented from undergoing decomposition while passine through the rangeof temperatures at wh ch decomposition tends to take place.

(at) The process should. be carried out under such conditions that thecombustible mixture ma not be diluted with inert gases, such as car ondioxide and water vapour, but may possess the maximum heat value perunit volume it has been hitherto proposed to carry out a process of thekind reierredto in the cylinder of an ordinary gas engine with a view tothe simultaneous production of power, but having regard to the necessityfor the fulfillment of the above conditions a gas engine such as isordinarily employed, in which the piston is controlled by a flywheel andconnecting rod, is unsuitable for the pur ose,

'lhe object of the present invention is to provide an improved method ofand apparatus for the production of nitric oxide,

whereby the optimum. conditions may be closely approximated and theyield from the process materially increased, and the invent-ion consistsin a process for producmg nitric oxide according to which an explosivemixture containing nitrogen and oxygen in suitable proportions isignited in a confined space produced by a partition on member which isfreely movable by the expansion of the gases following upon ignition,the supply of gases to, and the exhaust from, the combustion space beingcontrolled by suit-able means,

The invention also embraces apparatus for carrying out the aboveprocess, comprising a cylinder of differential diameters and havingadmission and exhaust ports, and a freely movable piston oicorresponding differential diameters within said cylinder and adapted tocontrol said ports,

The invention also embraces the method of and apparatus for producingnitric oxide hereinafter more particularly described.

Eigure 1 is a diagrammatic elevation partly in section showing one formof apparatus in accordance with the invention,

Figure 2 is a similar View showing the parts in greater detail and inpart sectional elevation.

In carrying my invention into effect in the manner illustrated, Iprovide a piston having difierential diameters and arrange the same toreciprocate within a cylinder constructed to form a series of coaxialportions of corresponding differential diameters, the arrangement beingsuch that the movements of the piston are conditioned only by work doneand energy stored and also by the use of elastic cushions.

Where it is desired that the apparatus should be seli-contained andadapted to measure, compress and supply its own combustible gas andscavenging air, 1 may construct the piston and cylinder with threediii'erential diameters, as shown, one end a of the piston being adaptedto be acted upon by the explosive gases within the cylinder 5, and theother end 0 to compress in the chamber d an elastic fluid which in turnperforms useful external work, intermediate annular spaces 6 7' beingformed by the movements of the central piston g'within the difi'erentialcylinders h i.

- such proportions that the mixture will not ignite until mixed in thecombustion space with a combustion supporter, such as air, supplied fromthe second annular space f.

*The inlets and outlets in the various parts of the cylinder may becovered and uncovered in appropriate sequence by the piston during itsmovements within the cylinder, thus permitting of the employment. ofsimple spring-controlled check valves in the passages communicating withsuch inlets and outlets.

When the apparatus operates upon the two-stroke cycle, the return strokefollowing a power stroke is effected by means of energy stored in one ormore elastic cushions which arepreferably made variable in capacity forpurposes of control.

ne or more of the combustible constituents is or are preferablypreheated to as high a degree as possible, and this may be effected bycausing the same to pass through a suitable heat intercha'nger orre-heater is Z by which they may abstract some of the sensible heat fromthe burnt products passing from the cylinder 6 through a large exhaustport m and a portion of such sensible heat may also be used to heat thecompressed air or other gas passing from the chamber cl before the gasis used for power purposes.

The scavenging of the apparatus must be as complete as possible in orderto prevent the combustible mixture from becoming diluted with inertgases, such as CO, and H 0, and the scavenging air and/or one or more ofthe combustible constituents may be compressed or stored under pressureduring one stroke in order to be employed during the succeeding stroke.

As shown in Fig. 2 the connected pistons a, g, 0, have rigidly attachedto them, tubes 1 and 2, of which the tube 1 is larger than the tube 2 sothat there is provided an annular space 3 between them by means of whichthe heated air which has cooled the pistons can find an exit.

The cold air enters at 4 and passing to the splayed end of the tube 2impinges upon the hottest part of the piston a, flows through theinterior of the pistons a, g, and c in sequence and finally passes outthrough the annular space 3.

The tube 1 slides in stufling boxes 6 and 7 and the tube 2 slides in theplpe 8, thus providing a closed pipe circuit for the scavenging air andpermitting this air to receive its first pre-heat before it enters theheater 1 where it is subsequently further re-heated.

The operation of the apparatus shown is as follows :Assuming that thepiston a is at the end of its stroke to the left and behind the pistonis a compressed charge of explosive mixture, the charge is ignited by anelectric spark in a manner to be described later and, thevalve n beingshut, the piston is driven under high pressure to the right. The gasesexpand until the left hand end of the piston a reaches the exhaust portm; this being a large port, the pressure falls rapidly and the exhaustgases passing downward through the tubular re-heater is Z and so to theabsorption apparatus where the nitric oxide is recovered. As soon as thepressure has fallen sufficiently, scavenging air stored under slightpressure in the pipe system 0 2, between the valves n and 9, opens thevalve n thus sweeping the exhaust gases towards port m, the, piston thencompleting its movement towards the right.

air is compressed in the chamber f and delivered past the valve gthrough the top half I; of the tubular re-heater into the chamber b anda little later the rich gas mixture from e, now under some pressure, isforced through the port 7' and valve 8 to mixwith the hot air in thechamber 6. The piston by its movement now closes the port mandcompresses the explosive mixture, the ignition of which commences afresh cycle,

Dealing with the operation in the cylinder h, the piston in travellingto the right takes in a rich gas mixture through the inlet valve 6 andthen on its return stroke to the left acts as a pump, pumping thismixture through the port 7' and valve 8 into the chamber b. The exactpressure at which the valve On the piston returning towards the left,

is opened may be determined by a spring on this valve.

When the port m is closed by the piston a, since the length of theremaining space in the cylinder h is greater than the remaining space inthe chamber 12 the pressure in b rises faster than in e and valve 8closes.

Chamber 7 with its piston c constitutes an ordinary air pump and whilethe piston is travelling to the right air is drawn into the annularspace f, past the non-return valve u, and when the piston travels to theleft this air is delivered past the valve 9 through the re-heater isinto the chamber b so long as port m is open. When this port closes, thepressure in b rises more quickly (due to the ratio of clearance spaces)than the pressure in f, so that valve n immediately shuts and the onlyeffect of the piston travelling further to the left is to store airunder some pressure in the pipe system between valves and n.

Considering now the operation in the chamber 12 when the piston moves tothe right, air is compressed and then delivered past the non-returnvalve '0 to the air pressure storagevessel (not shown). This delivery iscut off when the piston closes the port 10 and from this point the airis further compressed into the closed space at the Cit Leas es end of 0!until the kinetic energy of the moving piston is absorbed in raising thepressure of the enclosed air, thus bringing the piston to rest. Theenergy in this compressed air starts the piston in its movement to theleft again and imparts momentum to it until the air in the chamber (1has expanded to atmospheric pressure. From this point the further travelof the piston draws in fresh air through the inlet valve :2 during theremainder of the stroke.

Further in connection with the operation in chamber d it may be statedthat the volume of air compressed in this chamber by the piston 0 afterthe latter closesthe port w is sufiicient to absorb the remaining energy(mainl kinetic energy of the moving piston massg without exceeding adesired maximum pressure in 0?. Moreover any air volume remaininginchamber d after port w is closed, is theoretically capable ofabsorbing (and returning again) any energy remaining in the system. Ifthe volume is relatively small the pressure reached will be relativelyhigh and vice versa. Finally, during the movement of the piston to theleft, no expansive force is lost by escape of air through valve 2;,since said'valve does not open after the head 0 passes the port 10. U11expansion when 0 uncovers w on moving to the left, the pressure willhave fallen back at least to the same point where it stood in themovement of the piston to the right. Therefore, the pressure in d atthis point of time cannot exceed that on the delivery side of the valve1; and consequently this valve will not open.

In the drawing the compressed air is shown as passing through theheat-regenerator Z, but this merely indicates that a portion of the heatof the exhaust gas is used to increase the volume of the compressed airused for power. This air, however, should be heated after storage and onits way to the compressed air motors.

It will be observed that safety cushions exist in all the cylinders butmore especially in the left hand end of chamber 6 and the right hand ofchamber 03. These ensure the bringing of the piston to rest.

The apparatus is started by bringing the piston into such a positionthat it is about at its mid-stroke and then pumping into chamber b byhand an explosive mixture which is hand fired (electrically) so as togive the piston an initial movement to the right and to compress theelastic cushion in the end of the chamber d. The small inlet and outletin the chamber 5 necessary for this are not shown in the drawing. It maybe necessary to hold open the inlet valve 0: during the first stroke tothe right, but the action of the apparatus thereafter becomes automatic.

The speed of operation is controlled principally by the weight of thepiston (per unit area) and the equilibrium among the various indicatordiagrams is obtained by the proper proportioning of the sizes of thecylinders and the clearance spaces in the cylinders h and d.

A corresponding problem of this nature has been worked out in connectionwith the solid piston Humphrey pump, and pumps of this character areoperated with a free heavy piston at speeds from 60 to 250 cycles perminute, according to size. The mechanical problems do not, therefore,greatly diffor in kind from existing apparatus.

It should be understood that the acceleration of the piston when firstmoving to the right is very great, while the high pressure gases actupon it. Expansion is, therefore. more rapid than is possible in a gasengine where the piston travel has to conform with the movement of acrank and flywheel. The slowest part of the movement occurs towards theend of the travel of the piston to the right and this gives time for thescavenging gases to be passed through at a comparatively low pressure.Electrical ignition is secured by a contact device preferablg placed inthe cylinder f which is cold.

11 the form of apparatus illustrated, 9 represents an insulated plugadjustable axially by hand-wheel and screw, and 10 is a flexiblemetallic spring making contact with 9 when the pistons have moved farenough to the left. The binding screw 11 and the spring 10 are bothelectrically in contact with the metal parts of the apparatus and thecircuit containing the sparking plug which fires the mixture in space bis contained between 9 and 11, hence the circuit is completed when 9 and10 make contact thus causing a spark in space I) and sparking may beadvanced or retarded by rotating the hand-wheel which adjust the contact9. The spark is produced in the cylinder b somewhat before the end ofthe stroke, thus giving the maximum possible explosion temperature.Where the gases are preheated before compression. ignition (and preignition) may become spontaneous.

Where variable cushion capacity is provided such capacity mayconveniently be constituted in one or more vessels capable of sustainingthe required pressure and connected to such cylinder or part of the mainapparatus where the cushion is acted upon by the piston. Since thepressure to which the elastic cushion is raised by a given movement ofthe piston depends on the total cushion capacity the control of themovements of the piston will partly depend on this capacity which may beautomatically varied by pumping in or evacuating liquid which thusdisplaces more or less of the clastic medium.

Pivoted to the tube 1 at 12 are two links 13 and 14 which serve toconnect the levers ,15 and 16 which are respectively pivoted at 17 and18. The pivots at 17 and 18 are rigidly carried from the frame of theapparatus and form the stationary centres about which the levers 15and-16 oscillate as the pistons and tube 1 reciprocate. Attached to 15and 16 are weights 19 and 20 which are ad'ustable in position on thelevers and capa le of being fixed in any desired position along theirctive levers. These weights add to the reclprocating masses and theinertia so added will be greater as the adjustable weights areshiftedfurther from their respective pivots 17 and 18. This system of linkedweights therefore forms a means of adjusting the total inertia of thereciprocating system with the result that the speed of reciprocation ofthe apparatus may be controlled.

It is not considered necessary to describe in greater detail variablecushions or arrangements of linked weights because they are known fromBritish Patents Nos. 11818 and 28187 of 1911.

Investigation has shown that a higher yield of nitric oxide is obtainedas the concentrations of nitrogen and oxygen in the exhaust productsapproach a maximum thus indicating that the employment of oxygen toreplace some or all of the air will give greater yields of NO. A richgas is very much more effective than a poor gas and quite out ofproportion to the ratio of their calorific values. The method andapparatus is specially useful in combination with a process yieldingoxygen as a waste product for the utilization of a supply of oxygenwould give the maximum yield of NO with the present method.

It is to be understood that the foregoing details of'construction aregiven by way of example onl as I may form the apparatus such that t econversion only into nitric oxide will be performed therein, themeasurin and compressing of the constituents being effected by externalmeans, and the sion and exhaust ports, and a movable PIS,

ton of corresponding diameters within said cylinder and adapted tocontrol the said ports.

2. In the apparatus claimed in claim 1, the arrangement of a secondco-axial cylinder and an extension of the piston therein having adifferent diameter from the combustion cylinder and piston and soconstructed as to act as a pump vfor combustible mixture or aconstituent thereof.

3- :In the apparatus claimed in claim 1 the arrangement of a co-axialextension of the cylinder and piston having a difierent diameter fromthose mentioned in claim 1 and. so constructed as to act on one side ofthe piston as a pump for scavenging air and on the other side of thepiston as a com pressor of elastic fluid.

4:. In the apparatus claimed in claim *1, suitable ports in thedifferential cylinders adapted to be covered and uncovered by thepistonso as to permit the functions of the.

respective cylinders.

5. In the apparatus claimed in claim 1, a heat interchanger adapted toexchange heat between the exhaust gases and the scaveng ing air. 4

6. In the apparatus claimed in claim 1,

means of controlling the functioning by the aidof linked weights havingadjustable moments of inertia about their rocking centres.

In testimony whereof I have signed my name to this specification.

HERBERT ALFRED HUMPHREY.

